Send HTTP status code 400 for invalid requests

src/Server.php

@@ -84,10 +84,14 @@ public function handleConnection(ConnectionInterface $conn)
         });
 
         $conn->on('data', $listener);
-        $parser->on('error', function() use ($conn, $listener, $that) {
-            // TODO: return 400 response
+        $parser->on('error', function(\Exception $e) use ($conn, $listener, $that) {
             $conn->removeListener('data', $listener);
-            $that->emit('error', func_get_args());
+            $that->emit('error', array($e));
+
+            $that->writeError(
+                $conn,
+                400
+            );
         });
     }
 
@@ -123,4 +127,20 @@ public function handleRequest(ConnectionInterface $conn, Request $request)
 
         $this->emit('request', array($request, $response));
     }
+
+    /** @internal */
+    public function writeError(ConnectionInterface $conn, $code)
+    {
+        $message = 'Error ' . $code;
+        if (isset(ResponseCodes::$statusTexts[$code])) {
+            $message .= ': ' . ResponseCodes::$statusTexts[$code];
+        }
+
+        $response = new Response($conn);
+        $response->writeHead($code, array(
+            'Content-Length' => strlen($message),
+            'Content-Type' => 'text/plain'
+        ));
+        $response->end($message);
+    }
 }

tests/ServerTest.php

@@ -206,7 +206,6 @@ public function testParserErrorEmitted()
     {
         $error = null;
         $server = new Server($this->socket);
-        $server->on('headers', $this->expectCallableNever());
         $server->on('error', function ($message) use (&$error) {
             $error = $message;
         });
@@ -218,7 +217,38 @@ public function testParserErrorEmitted()
         $this->connection->emit('data', array($data));
 
         $this->assertInstanceOf('OverflowException', $error);
-        $this->connection->expects($this->never())->method('write');
+    }
+
+    public function testRequestInvalidWillEmitErrorAndSendErrorResponse()
+    {
+        $error = null;
+        $server = new Server($this->socket);
+        $server->on('error', function ($message) use (&$error) {
+            $error = $message;
+        });
+
+        $buffer = '';
+
+        $this->connection
+            ->expects($this->any())
+            ->method('write')
+            ->will(
+                $this->returnCallback(
+                    function ($data) use (&$buffer) {
+                        $buffer .= $data;
+                    }
+                )
+            );
+
+        $this->socket->emit('connection', array($this->connection));
+
+        $data = "bad request\r\n\r\n";
+        $this->connection->emit('data', array($data));
+
+        $this->assertInstanceOf('InvalidArgumentException', $error);
+
+        $this->assertContains("HTTP/1.1 400 Bad Request\r\n", $buffer);
+        $this->assertContains("\r\n\r\nError 400: Bad Request", $buffer);
     }
 
     private function createGetRequest()